1. Field of the Invention
The present invention relates to radio-wave receivers, radio-wave timepieces, and radio-wave reception integrated circuits.
2. Background Art
At present, standard radio waves including time codes are available in many countries including Germany, Great Britain, Switzerland and Japan in the world. In Japan, long-wave standard radio waves of 40 and 60 kHz amplitude-modulated with time code formats transmitted by two transmission stations installed in Fukushima and Saga prefectures are available. Each time a unit digit of a number indicative of minutes of correct time is updated, or at intervals of one minute, a time code of the radio wave is sent out in the form of a frame of 60 seconds.
At present, radio-wave timepieces are commercially available which receive the standard radio waves and correct the time that they count (hereinafter referred often to as “internal time” of the timepieces) (see TOKKAIHEIS 7-198878, 5-157859 and -142363 publications).
Generally, the radio-wave timepieces receive the standard radio waves at a predetermined time, for example at 2 o'clock, once per day. The reason for this is that time correction made substantially once per day suffices for accurate timekeeping in terms of an error involving the time counting and a time interval at which the time correction is performed. Reception of the radio waves at all times for time correction would increase power consumed in the radio-wave reception circuits of the timepieces.
However, with a radio-wave timepiece of the wristwatch type, power consumption is a problem that directly involves the continuously operable time of the wristwatch. Thus, even more reduction of the power consumption is required. To this end, various techniques are invented in which the operating time of the radio-wave reception circuit is minimized as much as possible. For example, an invention is known in which correction of the whole internal time by receiving the whole time code involving one frame included in the standard radio wave and correction of the “second” part of the internal time by using a signal called an M signal appearing when the time code is switched are selectively employed as requested (see TOKKAI 2000-235093 publication).
At least 60 seconds are required for receiving the whole time code. Actually, reception of the radio wave must continue for more than 120 seconds because a time required for the receiving operation of the radio wave reception circuit to be stabilized and a margin time required for receiving a time code for at least one frame should be considered. When the M signal described in TOKKAI 2000-235093 publication is received, the standard radio wave must be received continuously until the M signal is received and if the time required for the receiving operation of the radio wave reception circuit to be stabilized is considered, the reception of the radio wave must continue for a time corresponding to at least one frame. Thus, the time for receiving the standard radio wave is still large.
It is an object of the present invention to provide radio-wave receivers, radio-wave timepieces and time reception apparatus in which reduced time and hence power consumption are required for reception of the standard radio wave for use in time correction.